Patent GB-618062-A (GB)
Title: Improved control mechanism for supercharged aircraft engines
IPC: F02D29/00
Filed: 1946-05-22
Abstract: 618,062. Fluid-pressure servomotor control systems. GENERAL MOTORS CORPORATION. May 22, 1946, No. 15483. Convention date, June 11, 1945. [Class 135] In a control mechanism for a supercharged internal combustion engine for aircraft, the throttle valve is under joint manual and servomotor control to maintain a manually-selected pressure, and the control mechanism also varies the propellor pitch to maintain a selected engine speed relationship, which latter is variable manually without affecting the pressure selection. Actuation of the pilot's control lever rotates a shaft 35, Fig. 8, and a lever 38 carried thereby, the latter having a pin-andslot connection 43 with a floating lever 46 so that the latter will pivot about its connection with the rod of a spring-loaded servo-piston 66. Lever 46, through a link 48 and lever 50, rotates a shaft 51, and the latter, through levers and adjustable links outside the housing of the governor, opens the throttle a predetermined amount. The direct manual actuation of the throttle also selects a datum inlet pressure which the servomotor maintains automatically by its auxiliary control of the throttle, and this datum pressure is selected by a cam 121 carried by shaft 35. The cam is engaged by a follower 120 on one arm of a bell crank 106 with an eccentric bearing 109, the other arm being connected by a spring or rigid link 104 to a floating lever 101 which actuates a piston valve 95 controlling the servo-piston 66. Movement of the servo-piston is communicated to the throttle through floating lever 46, link 48, &c. Floating lever 101 is pivoted at its midpoint on a bridge connecting the movable end plates of bellows 132, 134 of which bellows 132 is subject to the pressure in the intake manifold of the engine or at the outlet scroll of the supercharger, and bellows 134 is evacuated. Both bellows are spring loaded, bellows 134 enclosing two loading springs, and the position of the fixed end-plate of bellows 134 can be adjusted initially by means of a screw. The movement of lever 38 is limited by stops 40. Loosely mounted on shaft 51 is a lever 154 which is spring-urged against a pin 150 carried by lever 50 so that, when the throttle is in wide-open position, the positions of shaft 51 and lever 50 will be such that lever 154 will be swung towards servo-control valve 95, and an abutment 156 carried by lever 154 will have pushed the valve into its neutral position to hold the servo-piston locked and prevent further movement being communicated to the throttle. When the pilot's control lever is shifted, the pitch of the propeller is also set through a lever 212, Fig. 15, carried by shaft 35, a cam surface 210 pivoted on lever 212, a bell-crank 200, and a piston valve 195 controlling a servo-piston 173 the movement of which is communicated to the propeller through a lever 167, shaft 160, &c. The control valve 195 is carried inside the rod of the servopiston so that the movement made by the piston will correspond to the impulse given to the valve. The valve is loaded by a spring 197 into contact with an abutment 196 carried by bell-crank 200, and this connection permits the variable pitch governor to be actuated manually when a rotary valve 181 is turned to cutoff the supply of pressure fluid to the servopiston and connect the latter to drain. Cam lever 210 is urged against a strut 216 by a spring 215, but contact between bell-crank 200 and lever 210 is normally maintained by a loading spring 206. A pin 240 carried by a pivoted lever 241 also abuts against lever 210, and rotation of lever 241 adjusts the position of cam lever 210 in such manner as to vary the response of the propeller pitch servomotor to give lowered engine speeds over the initial range of movement of the pilot's control lever. In a modification, rotary valve 181 is replaced by a piston valve actuated by a solenoid. The unit also incorporates a control for the variable speed gear in the drive of an auxiliary supercharger in response primarily to altitude as detected by an aneroid bellows 352, Fig. 28B. The datum of the latter can be set by adjustment of the position of the top end plate by means of nut 356 whilst the bottom, movable plate carries a floating lever 296 which actuates a valve 293 controlling a servo-piston 270. The latter is connected by a link 267 to a lever 262 pivoted on a stud (not shown), and a spring 260, connected between the junction of the link and the lever, has its other end joined to a lever 256 carried by a shaft 251 connected to the gear shift lever so as to constitute a toggle mechanism giving a snap change to the gear shift. This control of the gear shift can be removed by rotating a pin 370 to lift lever 296 and valve 293 so as to connect the servocylinder to drain, in which event spring 272 will force the servo-piston to the right to the low gear position. Lever 296 is also actuated by its contact with a cam 299 which is actuated, through a link 312 and a cam plate 310 carried on the same shaft as cam 299, when the manual control lever 38 is turned. The movement thus given to cam plate 310 partially controls the movement of a lever 318 which is pivoted on its lower end to lever 256. Lever 318 carries an abutment 320 which, when a gear shift into high takes place, abuts against and moves a lever 330 connected by a link 332 to eccentric bearing 109 so that the selected intake pressure is also varied.